Method and apparatus for immersion treatment of semiconductor and other devices

ABSTRACT

Method and apparatus for cleaning semiconductor devices and other workpieces using an aqueous rinse solution which is de-oxygenated by passing the aqueous rinse solution and a carrier gas through an osmotic membrane degasifier. A cleaning chamber is also disclosed for carrying out the cleaning method.

This is a division, of prior application Ser. No. 09/442,574, filed Nov.18, 1999, still pending which in turn is a continuation of applicationSer. No. 09/106,066, filed Jun. 29, 1998, now U.S. Pat. No. 6,021,791which are hereby incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to the aqueous processing of variousarticles, including the immersion cleaning of semiconductor wafers,using deoxygenated aqueous rinse solutions.

2. Description of the Related Art

As will be seen herein, the present invention is directed to the aqueoustreatment of a wide variety of commercially important articles, such asliquid crystal displays, flat panel displays, memory storage disksubstrates, as well as photographic plates and film. The presentinvention has found immediate commercial acceptance in the field ofsemiconductor wafers, especially wafers of a type which are ultimatelydivided to form a plurality of electronic devices.

During the course of producing commercial semiconductor wafers, layersof various materials are built up on one surface of a wafer blank. Thesevarious layers are processed using several different etching techniques,each of which results in a residue which impairs further devicefabrication. It is important that such residues be effectively removed.Typically, the several types of residue are removed with solventsespecially adapted for the particular residues. While such solvents aregenerally effective for removing residues, solvents remaining on thesurfaces of the semiconductor device also impair further devicefabrication steps.

Accordingly, it is important that the solvents be removed from thesemiconductor device and it is known that water rinsing is an efficientmeans of solvent removal. However, semiconductor device layer materialshave changed over the years, and presently semiconductor devicemanufacturers are employing materials which are subject to corrosionupon contact with water. In an effort to reduce the corrosion problem,carbon dioxide gas has been sparged, i.e., bubbled, into the rinse waterto partially lower the pH of the rinse water. However, bubbling carbondioxide into water rinses used in the semiconductor device fabricationindustry has proven to be only marginally successful in reducing theextent of corrosion, and further adds the risk of introducingcontaminating particles into solution. In an effort to overcome growingproblems of corrosion, the semiconductor device fabrication industry hasinvestigated intermediate rinse steps using non-aqueous rinse solutions.However, such non-aqueous solutions have proven to be less effectivethan rinse water in removing solvents and wafers are still routinelyrinsed with water, despite the corrosion effects.

Significant efforts have been expended in reducing the amount ofexposure of a wafer containing alloys of copper and aluminum to rinsewater. However, it appears that, in order to meet future requirementsfor improved electrical performance, the aluminum content of the alloymust be substantially reduced and possibly eliminated, thussubstantially increasing the susceptibility of the wafer layer materialsto corrosion, at higher levels than those presently experienced.

One example of efforts to improve wafer production involves oxygenremoval to reduce oxide growth on the surface of semiconductor wafers.For example, literature describing the PALL SEPAREL Model EFM-530Degasification Module addresses the reduction of dissolved oxygen indeionized water, in a manner which avoids potential defects tosemiconductor devices caused by the formation of unwanted oxide layers.As is known in the art, an oxide layer forms when pure silicon isexposed to an oxygen source, such as dissolved oxygen in a rinse wateror other aqueous medium. The oxide layer can change the surface of thesilicon from hydrophobic to hydrophlilic, a condition which isundesirable in some aspects of wafer processing, such as pre-diffusioncleaning operations. Accordingly, the PALL Degasification Moduleaddresses the need to deoxygenated rinse water to avoid formation of asilicon dioxide layer in the rinse after the wafer is treated with an HFetch solution. As can be seen, the problem addressed by the PALLDegasification Module is not related to problems encountered incontrolling corrosion of aluminum, such as pitting and etching, as hasbeen experienced in processing wafers carrying copper/aluminumstructures on their surface. While dissolved oxygen is alsoobjectionable from a corrosion standpoint, the corrosion problem is notconcerned with the formation of unwanted oxides. A further, morecomplete system control over wafer processing so as to reduce corrosionin wafers containing copper/aluminum structures is needed.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide cleaning forsemiconductor wafers using aqueous solutions which are treated in amanner to eliminate corrosion of semiconductor device materials layeredon semiconductor substrates.

Another object of the present invention is to provide cleaning of theabove-described type which is effective even in relatively small, hollowstructures formed in a semiconductor surface, such as vias.

A further object of the present invention is to provide aqueoustreatment of the type described above which removes dissolved oxygenfrom an aqueous solution while controlling the pH of the aqueous,solution.

Another object of the present invention is to provide arrangements foraqueous treatment of many different types of devices using conventionalreadily obtained equipment, and consumables which are relativelyinexpensive.

Yet another object of the present invention is to provide processarrangements of the type described above by employing an osmoticmembrane degasifier and using a carrier fluid (preferably a gas)comprised of one or more components, preferably for oxygen removal and,optionally, pH control or other chemical adjustment to the aqueoussolutions.

These and other objects according to principles of the present inventionare provided in apparatus for processing a workpiece, comprising:

a cleaning chamber defining a cavity for receiving the workpiece and adevice opening through which said workpiece is passed into and out ofthe cavity;

an osmotic membrane degasifier defining a degasifier cavity, a membranedividing the degasifier cavity into first and second parts, a aqueoussolution inlet and a aqueous solution outlet associated with said firstpart to direct aqueous solution into contact with one side of themembrane, and a carrier gas inlet and a carrier gas outlet associatedwith said second part to direct carrier gas into contact with the otherside of the membrane;

and the aqueous solution outlet coupled to the cleaning chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevational view of cleaning apparatus according toprinciples of the present invention;

FIG. 2 is a schematic plan view thereof;

FIG. 3 is a cross-sectional view taken along the line 3—3 of FIG. 2;

FIG. 4 is a schematic diagram thereof; and

FIGS. 5-8 show a sequence of operation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As mentioned above, the present invention has found immediateapplication in the field of semiconductor device fabrication. However,in providing methods and apparatus for carrying out controlled immersionprocessing operations as well as providing deoxldized and/orpH-controlled aqueous solutions, the present invention is readilyadaptable to a wide range of commercially significant activities, suchas the photographic processing of plates, films and prints, and thefabrication of liquid crystal and flat panel displays, as well asarticles requiring highly refined surface finishes, such as hard diskmemory substrates. As will be seen below, the present invention will bedescribed with reference to the processing of semiconductor wafers,although it will become readily apparent to those skilled in the artthat other types of workpieces other than semiconductor wafers andimmersion processing other than aqueous cleaning and/or rinsing ofsemiconductor wafers is also encompassed within the scope of the presentinvention.

Semiconductor wafers are typically fabricated by forming a layeredseries of devices integrated with an underlying semiconductor blank orso-called “prime wafer”. With the formation of each layer, the wafer inprocess must be polished and cleaned in preparation for the nextlayering step. With ongoing changes in layer materials, new, challengingprocessing problems have arisen. In general, the unit cost of individualwafers is increasing dramatically and, accordingly, even partial lossesof wafers being processed result in an expensive penalty for the waferfabricator. Unwanted materials, such as contamination particles andresidues associated with via etching or metal etching processes, cancause subsequent layering operations to fail. Such residues andcontamination particles associated therewith are typically removed usingvarious solvents. The solvents are then removed with one or more rinsesolutions, and the present invention has found immediate acceptance inproviding aqueous solutions (i.e., solutions whose composition is eitherexclusively or predominantly comprised of water) for use in suchcleaning and especially in rinsing operations.

Increasing use is being made of device layer materials (such asaluminum/copper alloys and proposed all-copper structures) which havegreater susceptibilities to corrosion when exposed to water rinses.However, as is widely recognized, here are strong advantages inemploying aqueous solutions for wafer rinse. For example, compared tonon-aqueous rinses (i.e., rinses not predominantly comprised of water),such as isopropyl alcohol (IPA) or N-methyl pyrrolidone (NMP), aqueousrinse solutions require less investment cost, less safety precautions,are more affordable to dispose of when their useful life has expired,and for many types of popular solvents, aqueous solutions are the mosteffective rinsing agents for cleaning the wafer surfaces beingprocessed.

In developing the present invention, consideration was given to thecorrosion mechanisms typically encountered in semiconductor waferprocessing. For example, the corrosion of aluminum was studied withreference to the following oxidation/reduction reactions:

(Equation 1) 4Al →4Al²⁻+12e⁻

(Equation 2) 6H₂O+3O₂+12e⁻12OH⁻

(Equation 3) 4Al+3O₂+6H₂O→4Al(OH)₃

(Equation 4) 4Al(OH)₃→2Al₂O₃+6H₂O

Equations 1 and 2 describe the reactions driving the formation ofcorrosion and corrosion byproducts reflected in Equations 3 and 4. Aswell be seen herein, the approach of the present invention is to removethe oxygen reactant. Further, it is observed that the corrosion ratesare affected by the pH of the aqueous solution. One objective of thepresent invention is to combine both pH control and oxygen removal toform a combined one-step treatment of the aqueous solution brought incontact with the wafers being processed.

Referring now to FIGS. 1 and 2, a wafer treatment apparatus according toprinciples of the present invention is generally indicated at 10.Apparatus 10 includes a process chamber 12 surrounded by relatedequipment, to form a practical wafer-treating operation. As can be seenin FIG. 2, a robot load/unload area 14 is located adjacent or above theprocess chamber and includes conventional robotic placement equipment(not shown) for inserting and removing semiconductor wafers from processchamber 12. Reference numeral 16 is directed to a portion of wafertreatment apparatus 10 which includes an uninterruptable power supply(UPS) and control means, including a computer, and electronicsinput/output capability which is accessed by switches and other controls18 located on the outside of the enclosure cabinet, as can be seen, forexample, in FIG. 1.

Turning now to FIG. 3, the process chamber 12 is shown in greaterdetail. Although different processes can be carried out with chamber 12,it has found immediate application for immersion cleaning (includingrinsing and drying) of semiconductor wafers, such as wafer 22 shown inFIG. 3. Chamber 12 includes a body generally indicated at 24 comprisinga receptacle 26 and an outer, surrounding enclosure 28. Body 24 definesa hollow interior 30 which preferably is hermetically sealed andexhausted to a suitable control system.

Receptacle 26 is preferably made of quartz material or othernon-reactive material and is formed to define a wafer-receiving cavity34 having an upper opening 36 through which wafers or other workpiecespass as they are inserted and removed from cavity 34. A weir opening 38is formed adjacent the upper end of receptacle 26 and directs overflowin a manner to be described below with reference to the schematicdiagram of FIG. 4. One or more wafers 22 are supported at their bottomedge on furniture or support members 42 located adjacent a passageway 44communicating with a plenum 46 which is located beneath body 24. A fastdrain valve 48 is located at the lower end of plenum 46.

As can be seen in FIG. 3, passageway 44 connects cavity 34 with aninterior volume 52 of plenum 46. A fast flow valve 60 and a slow flowvalve 62 communicate with interior 52 and are operated to fill plenum 46with an aqueous medium, preferably deionized water treated in a mannerto be described herein. Also coupled to the interior 52 of plenum 46 isa fast flow valve 66 and a slow flow valve 68, used to fill plenum 46with a chemical, such as solvents or a non-aqueous rinse solution, suchas isopropyl alcohol (IPA). In operation, plenum 46 is first filled witha desired solution, with the level eventually rising past passageway 44to enter cavity 34. The liquid level may be maintained within quartzreceptacle 26 at any step of a process or may intentionally causeoverflow to pass through overflow weir 38. Preferably, workpieces andsolutions within receptacle 26 are excited by conventional means, suchas sonic, preferably ultrasonic or megasonic transducers 102, to enhancethe cleaning or other processing operations.

An upper wall 72 of body 24 includes a recess for a conventional sealinggasket 74. A plurality of lids, preferably two lids and most preferablythree lids, are hingedly joined to body 24 adjacent upper surface 72 andare selectively movable, one at a time, to sealingly enclose the upperend 36 of receptacle 26. As will be seen herein, each lid is operable toenclose cavity 34 to provide a wide range of environments within thereceptacle cavity. For example, processing lid 80 hingedly connected at82 to body 24 is closed during cleaning or other processing of wafer 22.In order to prevent condensation on the lid inner surface 84, lid 80 isprovided with a blanket heater 86. It is generally preferred that thelid 80 confine a pressurized gas blanket on top of the liquid surfacewithin cavity 34. The gas blanket is introduced into the cavity byconventional nozzle means in the process lid or cavity wall. The gasblanket can be comprised of a suitable non-reactive purge gas, such asnitrogen, or, if desired, can be comprised of carbon dioxide so as toprovide additional pH control if the liquid surface within cavity 34 isbroken, as during a rapid cavity-filling operation. Optionally, theprocessing lid 80 can include apparatus for purging ambient environmentfrom cavity 34 preparatory to a processing operation.

Drying lid 90 is lowered to engage gasket 74 and enclose upper opening36 of cavity 34 during wafer drying operations. Lid 90 preferablyincludes conventional wafer drying equipment of the “MARANGONI” orsurface tension gradient drying type, but other types of dryingapparatus, such as heat lamps, super heated vapor, or spin drying canalso be used. One example of drying lid 90 is given in U.S. Pat. No.5,634,978, the disclosure of which is incorporated by reference as iffully set forth herein.

The preferred lid 90 includes an assembly 92 of nozzles injecting afinal rinse solution, preferably one having a relatively low vaporpressure, such as isopropyl alcohol, and a heated inert drying medium,such as nitrogen gas. A third, load lid 94 is used during load/unloadoperations and includes an inner surface on which wafer cassettes,carriers or other load/unload equipment may be temporarily placed.However, if working surfaces are otherwise provided, or if sufficientlycapable robotic equipment is used for loading and unloading, lid 94 maybe rendered unnecessary and can be omitted, if desired.

Referring a gain to FIG. 2, various components associated with thedrying equipment located in assembly 92 are identified in FIG. 2 byreference numeral 106. The components 106 are coupled by means notshown, to assembly 92 in lid 90. As mentioned, valves 60, 62 introduceaqueous media into receptacle 26. In order to provide improved controlover oxidation reactions with layered, copper-bearing structures carriedon wafer 22, the aqueous media in contact with wafer 22 is, according toone aspect of the present invention, treated by an oxygen filter in theform of an osmotic membrane degasifier indicated by reference numeral108 in FIG. 2. The aqueous media (preferably conventional deionizedwater) is passed over a semi-permeable membrane, such as membranesavailable from Hoechs. Celanese for use with their LIQUI-CEL MembraneDegasifier, the osmotic membrane degasifier preferred in carrying outthe present invention. Similar osmotic membrane degasifiers may also becommercially obtained from Pall Corporation of East Hills, N.Y., underthe trade designation “SEPAREL” and W. L. Gore & Assoc. in Elkton, Md.under the trade designation “DISSOLVE”.

The aqueous media is passed over one side of the semi-permeable membranein degasifier 108 while a carrier fluid, preferably a gas at apre-selected temperature and pressure, is caused to flow over theopposite side of the semi-permeable membrane. The preferred carrier gas,according to the principles of the present invention, may be comprisedof one or more components and preferably carries out several purposes.First, the carrier gas “carries” or “pulls” dissolved oxygen from theaqueous media being treated. Thus, oxygen (or other dissolved gas) fromthe aqueous media is made to selectively diffuse across thesemipermeable membrane so as to enter the carrier gas stream located onthe opposite side of the membrane. Preferably, the flow of carrier gasis set so as to maintain the highest practical diffusion rate across themembrane, preventing oxygen levels on the carrier gas side of themembrane from reaching equilibrium with the carrier gas.

Optionally, the carrier gas is selected for its ability to diffuse in areverse direction across the semi-permeable membrane, so as toquiescently inject beneficial additives into solution in the aqueousmedia. Most preferably, the carrier gas is selected such that, upondissolving in the aqueous media it will act to alter the aqueous mediapH value in a manner which further precludes corrosion of the waferstructures. The preferred carrier gas of the present invention comprisesa mixture of two gases, one for causing dissolved oxygen in the aqueousmedia to flow across the osmotic membrane and the second to alter the pHvalue when introduced into the aqueous media. The first component can becomprised of virtually any gas or liquid other than oxygen so as tocreate the desired osmotic pressure across the membrane, and the secondcomponent most preferably comprises carbon dioxide, but may alsocomprise ammonia, nitrous oxide, nitric oxide and carbon monoxide. Thus,preferably, the carrier gas of the present invention employed for usewith semiconductor materials comprises a mixture of carbon dioxide andnitrogen gas. This carbon dioxide mixture is one example of a carriergas meeting one requirement of the present invention, that of “pulling”oxygen from the aqueous media through the semi-permeable membrane, whilepassing an effective pH modifier through the membrane in an oppositedirection.

The carrier gas can provide further functions. For example, it has beenobserved that gas entrained in the aqueous media provides a moreefficient coupling of agitation energy, such as sonic energy, includingenergy at ultrasonic and megasonic (i.e., megahertz) frequency regimes.As pointed out above, dissolved oxygen can be a poor choice foragitation enhancement. However, with the present invention, a benign gascan be dissolved in the aqueous media, upon its passage through heosmotic membrane.

Once in solution with -he aqueous media, the carbon dioxide emergingthrough the membrane removes OH⁻ shown in the above equations, andespecially Equation 3. However, unlike carbon dioxide sparging orbubbling, potentially contaminating particles are not introduced intothe wafer-contacting aqueous media. Further advantages over spargingtechniques are also made possible by the present invention. For example,by passing through the semipermeable membrane of the present invention,carbon dioxide is introduced into the aqueous media in a finer, i.e.,physically smaller, form. Accordingly, carbon dioxide is more completelydissolved in the aqueous media and is more quickly and thoroughly mixed.Further, with the present invention, carbon dioxide is introduced intothe aqueous media quiescently, without bubbles. In addition to slowingor otherwise impairing dissolving of the encapsulated CO₂ gas, bubblesintroduced by sparging or the like bubbling technique might be carriedto the wafer surface to form an effective barrier, at least partlyblocking intimate contact of the wafer surface with the treatingsolution.

In order to provide a wide range of control of pH values, the preferredcarrier gas, as mentioned, comprises a mixture of carbon dioxide and adiluent, such as nitrogen gas, which allow, the oxygen transfer rate tocontinue across the membrane while holding the aqueous media pH value ata constant level. As can be seen from the above, the CO₂ gas isintroduced into the aqueous media to provide pH control. The presentinvention also contemplates the introduction of chemicals passingthrough the osmotic membrane to achieve desired objectives other than pHcontrol. For example, a desired surfactant may be introduced in liquidor gaseous form in the carrier stream and, upon passing through theosmotic membrane, will be quiescently added to the aqueous media. Ifdesired, additional control may be provided by employing other,conventional pH control methods directly in the process chamber. Forexample, a carrier gas mixture of 4% hydrogen gas and 96% nitrogen gascan be used to provide a more reducing environment, which is less likelyto permit corrosion. As a further example, an injection apparatus can beprovided within cavity 34 to introduce a buffer or ion exchangesolution. Optionally, an acid or base drip can be added to one of thelids covering the cavity.

In addition to the above equations, consideration is also given to theincreasing use of copper and copper alloys as structures layered onsemiconductor substrates. From a device manufacturer's standpoint,increased copper content provides increased conductivity and henceincreased speed of electronic operation. The demand for copper contentof copper/aluminum alloys is steadily increasing and it is possible thatmetal lines formed on semiconductor substrates may be comprised entirelyof copper metal. As is well known, even small percentages of copperundergo substantial corrosion when contacted with water containingdissolved oxygen. When such small amounts of copper (components greaterthan 1% of the total alloy) are added to aluminum, an observed galvanicreaction between copper and aluminum operates to seriously increase thecorrosion rate of the aluminum component.

Equation 5 3Cu₁₈: +Al_((s))→Cu^(δ−)Al^(δ−)

Once the aluminum component becomes positively charged, the electronsare attracted in the p-orbital of the rinse water O₂ molecule. Byeffectively removing dissolved oxygen from the aqueous media, thepresent invention eliminates these types of corrosion reactions.

It has also been observed in carrying out the present invention, thatthe corrosion reaction rate displays photochemical sensitivity. Attemptsto quantify the photoreactivity of the various corrosion reactions havenot been studied in detail, but even so, the observed photoreactivityrole is pronounced in conventional semiconductor cleaning operations.The process chamber 12 is constructed such that the interior ofreceptacle 26 is sealed in a light-tight as well as an air-tightcondition, using lids which carry out multiple functions beyond merelyblocking ambient light.

As mentioned above, wafers 22 to be processed may be sprayed, but arepreferably immersed in solution contained within receptacle 26. Thisprovides several advantages. Due to the chemical sensitivity ofmaterials employed, and ever tightening constraints on processparameters, management of so-called “backside” wafer contamination isbecoming increasingly important if wafer losses are to be controlled. Byproviding an immersion cleaning of wafers 22, issues of backsidecontamination are eliminated in a cost effective rapid manner, since allexposed surfaces of the wafer are cleaned simultaneously.

Further, with the present invention, dislodged particles are managedwith greater control so as to prevent their re-introduction on the wafersurface. For example, referring to FIGS. 2 and 4, tanks 10, 112 arelocated adjacent process chamber 12 and are coupled to the processchamber with a plurality of supply and return lines. Tank 110 is coupledto plenum 46 by a return line 116 and by a supply line 118 whichincludes a pump 120 and filter 122. A second return line 124 couplestank 110 to weir outlet 38. Tank 112 is connected to plenum 46 throughreturn line 126 and through supply line 128 associated with pump 130 andfilter 132. A second return line 134 couples tank 112 to weir outlet 38.Tanks 110, 112 have supply inlets 140, 142 to a bulk chemical source(not shown).

Referring to the bottom right corner of FIG. 4, a deionized water inlet150 and a carbon dioxide mixture inlet 152 are provided for the osmoticmembrane degasifier 108. The carbon dioxide mixture or other carrier gasentering inlet 152 passes across the membrane internal to degasifier 138and exits through exhaust 154. A portion of the carrier gas, along withthe water introduced by inlet 150, exits through line 156 which iscoupled to valves 60, 62. Preferably, inlets 150, 152 includetemperature control (e.g., heating capability coupled to controller 304.In addition to providing control of the aqueous media in cavity 34,heating control at inlets 150, 152 controls the diffusion rates andbi-directional selectivity of the osmotic membrane.

Referring to the upper right-hand portion of FIG. 4, drying equipment106 includes a rinse agent tank 160 and a pump 162 which are coupled toassembly 92 mounted in lid 90. As mentioned, the rinse agent preferablycomprises isopropyl alcohol. The drying gas, preferably N₂, entersthrough inlet 164 and is heated in heater 166, thereafter beingconducted through line 168 to assembly 92 in lid 90.

As noted above, it is preferred that all wafer-contacting chemistriesare introduced into cavity 34 from plenum 46. In this arrangement,points of entrapment are eliminated as are direct chemical connectionsto receptacle 26, thereby avoiding the attendant possibility ofmis-operation. As will be seen below, it is generally preferred thatcavity 34 be operated as a recirculating immersion process chamber aswell as an overflow immersion rinse bath. Although not preferred for thetreatment of semiconductor wafers, cavity 34 can be operated in a spraycontact or waterfall mode, with conventional nozzles located in theinterior of cavity 34 and/or the lids associated therewith.

As can be seen from the above description of FIG. 4, severalrecirculation loops are provided with the arrangement of the presentinvention and it is contemplated that the treatment apparatus maycomprise a totally closed system. However, it may also be advantageousfrom time to time to discard certain portions of the processing orrinsing agents employed and connections to an industrial waste waterdrain are provided by line 172 (exiting a manifold at the outlet ofplenum 46) and line 174 (coupled to the weir discharge 38). Connectionsto a separate solvent drain are provided by line 176 exiting plenum 46and line 178 coupled to tank weir outlet 38.

As will be appreciated from the foregoing, chamber 12 can be operated ina number of different ways. For example, wafer treatment can be limitedto post solvent wafer rinse. However, it has been found unnecessary toperform residue-removing solvent cleaning at a separate location.Rather, residue is preferably removed from the wafer using solvent inchamber 12, followed by a solvent--removing rinse and concluding with awafer drying operation. Initially, cavity 34, passageway 44 and plenum46 are emptied, cleared of all liquids. If desired, a purge gas can beemployed, filling the cavity, passageway and plenum.

In preparation for a wafer transport operation, load lid 94 is openedand one or more wafers 22 are inserted in cavity 34, so as to rest onfurniture supports 42. In an optional pre-treating step, the emptyplenum 46 is then filled with a first solvent solution, preferably takenfrom tank 110 and passed through filter 122. Solvent is introduced so asto eventually fill plenum 46, passageway 44 and the interior or cavityof receptacle 26. Tank 110 preferably contains used solvent, capturedfrom a previous secondary solvent cleaning operation, as will be seenherein. This initial contact with the wafer causes the highestconcentration of residue and contaminating particles to enter intosolution within cavity 34. It is anticipated that, in many commercialoperations, this initial pre-treatment solution will be discarded.Depending upon the flow conditions within cavity 34, the initialpre-treating solution may also exit cavity 34 through overflow weir 38.Alternatively, cavity 34, passageway 44 and plenum 46 may be drained byline 176.

In certain instances, the pre-treatment operation may be unnecessary, inwhich case pump 120 is energized so as to withdraw used solvent fromtank 110, which, after exiting filter 122, fills plenum 46 andultimately cavity 34. After a sufficient period of ultrasonic agitation,the solvent is either returned to tank 110 through line 116 or isdischarged to the solvent drain through line 176. It is generallypreferred during all stages of wafer cleaning that wafer 22 bemaintained fully immersed and further that cavity 34 be filled so as tocause a controlled overflow through weir 38. Overflow solvent can bereturned to tank 110 through line 124 or the overflow can be dischargedto solvent drain through line 178.

If desired, conventional particle counters 300 (see FIG. 4) such asthose commercially available from Particle Measuring Systems (PMS)located at Boulder, Colo. can be employed to monitor contents of cavity34 to aid in the decision whether to retain or discard the overflowand/or the cavity contents. Alternatively, conventional chemicalmonitoring systems 302 may be coupled to controller 304, to sample theweir overflow to detect the presence or concentration of a residuecomponent in order to provide information to controller 304 indicatingthe real time concentration of residue in solution. Such indications canbe used to detect when rinsing of solvent is complete. According to theconcentrations of residue indicated, the overflow residue can, underoperation in controller 304, be either retained in Lank 110 ordiscarded. Output indications can also control any amount ofcontamination—diluting fresh chemistry that may be added to tank 110through line 140.

At the conclusion of the first cleaning stage, with the reused solventbeing withdrawn from the plenum 46 and tank cavity 34, “cleaner” solventin tank 112 is passed through pump 130 and filter 132 to plenum 46 andthe level is allowed to rise, filling cavity 34, fully immersing wafer22 and causing a controlled overflow through weir outlet 38. Weiroverflow may be returned through line 134 to tank 112 or may bedischarged to a solvent drain through line 178. At the conclusion of thesecond stage of wafer cleaning, the wafer may be immersed, sprayed,washed or otherwise “reused” with virgin solvent from a bulk supply. Thetank cavity passageway 44 and plenum 46 are then drained of all solvent.The solvent is preferably returned to tanks 110 and/or 112 through lines116, 126 but may be discharged to a solvent drain through line 176, ifdesired.

Thereafter, wafer 22 is rinsed with an aqueous rinse solution to removesolvent-from the wafer surface, wafer cavities and other structurescarried on the wafer substrate. An aqueous media such a deionized wateris processed in osmotic membrane degasifier 108, as described above. Aflow of deionized water enters through inlet 150 and a flow of carbondioxide carrier gas enters the degasifier through inlet 152. Oxygenenriched carrier gas exits degasifier 108 through line 154 and theoxygen-depleted, pH-balanced deionized water exits degasifier 108 online 156. The aqueous solution, thus treated, may be stored on site, ifdesired. Preferably, however, the aqueous solution is used on demand, asneeded. As with other solutions contacting the device being treated, themodified deionized water fills plenum 46, passageway 44 and cavity 34,immersing wafer 22. Preferably, a controlled overflow is maintainedthrough weir opening 38, being directed through a manifold coupled toexit line 174, thereby being passed to an industrial waste water drain.If desired, overflow can be filtered and redirected through pumping (notshown) to a deionized water reclaim inlet 186, although this has beenfound to be unnecessary due to the cost efficiencies of employingdeionized water as a rinse agent.

Turning now to FIGS. 5-8, the preferred solvent exposure will be brieflyconsidered. FIG. 5 shows an initial wafer contacting operation in whichreused solvent from tank 110 fills cavity 34. This initial contact withthe wafer contains the majority of dissolved polymer, with polymerconcentrations substantially higher than those found in tank 110.Accordingly, it may be desired to discharge the initial contactingsolvent to the solvent drain as indicated. Thereafter, the overflowsolvent is recirculated back to tank 110 and preserved for reasons ofeconomy. If desired, the solvent could also be directed to a suitablesolvent drain.

Although the solvent represented in FIG. 6 is reused and thereforecontains certain concentrations of dissolved residues, theconcentrations of residue are relatively small compared to theconcentrations obtained upon initial wafer contact as considered abovewith reference to FIG. 5. It is generally preferred that most, if notall, of the residues on the wafer be removed in the step indicated inFIG. 6, i.e., with reused solvent.

Only after the residues are removed from the surface of the wafer beingtreated is cleaner solvent applied to the wafer, as indicated in FIG. 7.Use of fresh solvent eliminates the possibility of dropping dissolvedpolymer residue out of solution or interrupting the suspension ofpolymer in solvent which is not yet filtered. The preferred purpose ofintroducing cleaner solvent from tank 112 is to remove dirty solventprior to recirculating the chemistry. As indicated in FIG. 7, it ispreferred to capture the “cleaner” solvent from tank 112 in tank 110,for use on the next cleaning cycle.

As will be appreciated, the chemistry now present in contact with thewafer is cleaner than conventional dual tank bench configurations,because the volume within the tank is continually topped off with freshchemistry from a bulk source. As can be seen from the diagram of FIG. 4,it is also possible to use virgin solvent chemistry exclusively, priorto the aqueous rinse step.

Referring to FIG. 8, as a final solvent cleaning step, fresh, unusedsolvent is introduced and recirculated with respect to tank 112. It ispreferred that solvent filling the cavity, passageway and plenum arereturned to tank 112 for future use. Thereafter, the aqueous rinse anddrying steps described above are carried out. During this time, tank 112is “topped off” from a bulk solvent source, if desired. As will beappreciated, fresh solvent introduced into tank 112 will have benefit ofa substantial residence time for any desired mixing, heating, or othertemperature control prior to its application in a subsequent processcycle.

In order to maintain the proper chemical component ratios of the solventas long as possible, the present invention allows the cleaning step tobe carried out with a minimum exhaust and purge, which might otherwisecause a loss of quality or quantity of solvent due to evaporation ordecomposition associated with oxygen and water content in surroundingair. Thus, as can be seen, the present invention provides improvedchemistry management by controlling the chemistry environment during acleaning operation.

As has been noted above, certain variations and alternative arrangementsare possible with the methods and apparatus according to the principlesof the present invention. If desired, other alternative arrangements canalso be readily employed with the present invention, using conventionalequipment and techniques. For example, operation of the osmotic membranedegasifier 108 can be automated using conventional techniques so as tominimize consumption of carrier gas. For example, as mentioned, it ispreferred that a mixture of carbon dioxide and nitrogen gas be used forthe carrier, at a flow rate which assures adequate diffusion rates ofoxygen across the membrane.

If desired, conventional metering 308 to sense dissolved oxygen can beprovided on line 156 and the flow rates of the carrier gas at inlet 152can be adjusted with control signals applied to N₂ and CO₂ flowcontrollers 312, 314, respectively. For example, if objectionable oxygenlevels are detected in line 156, the flow rate of carrier gas can beincreased in order to increase osmotic pressure, thereby withdrawinghigher rates of dissolved oxygen from incoming aqueous solution. On theother hand, if dissolved oxygen content in line 156 is sufficiently low,it may be possible to reduce the input flow of one or more carrier gascomponents and still achieve the desired levels of oxygen removal inline 156.

Further, related variations are also possible. For example, the carbondioxide and nitrogen components of the carrier gas can be mixed asneeded and fed into inlet 152. Conventional pH meters can beincorporated in metering 308 to sense the pH of aqueous media in line156 and the CO₂ component of the carrier gas can be adjusted byoperation of flow controller 314 to attain the desired pH level. Anyundesired reaction in osmotic pressure (needed to remove dissolvedoxygen) can be effectively dealt with by independently adjusting thenitrogen gas flow component (by signals to flow controller 312), sinceboth carbon dioxide and nitrogen gas components of the carrier gas areeffective in maintaining the desired osmotic pressure needed foreffective oxygen removal from the aqueous solution in degasifier 108. Ifdesired, the pH monitoring output and dissolved oxygen monitoringoutputs from metering 308 can be Considered together either by anoperator or more preferably by computer controlled automation 304 tovary the flow rates of the components of carrier gas entering inlet 152.Of course, such automated control could operate to prevent aqueous mediain line 156 from entering process chamber 12 if the dissolved oxygenand/or pH levels exceed predefined control points.

As mentioned above, particle counters 300 and chemical monitoringsensors 322 of predictors indicating the concentration of dissolvedresidue can be employed in cavity 34 or in the effluent of overflowexiting weir 38. As indicated in the above discussion, it iscontemplated that automated control attention be given to the varyingconcentrations of contaminant particles and residue levels in cavity 34,and that control steps be taken to segregate (preferably discard)materials containing unacceptably high concentrations of contaminantparticles and/or dissolved residue.

Contaminant levels (either particles or dissolved residue) can beestimated based on their residence time in contact with the wafer orother workpieces immersed within cavity 34. For example, considerationis given to the fact that the material filling cavity 34 be inputted inthe plenum 46 at a rate so as to assure a desired rate of overflowpassing through overflow weir 38. Overflow materials initially appearingat weir 38 can, for an initial period of time, be diverted away from arecirculation loop or storage container and thus be prevented fromcoming into contact with lesser-contaminated solution.

However, using conventional automation techniques, greater efficienciescan be obtained by directly monitoring the contamination levels withincavity 34 and/or effluent from overflow weir 38. Particle countersand/or automated chemical monitors of dissolved residue can be employedto provide a more efficient use of solution by preventing theunnecessary disposal of solution initially contacting the wafer surface.In this manner, greater flexibility of operation is possible and wafersof differing compositions and surface properties can be accommodatedwith a single routine production schedule.

Further, with the introduction of automated metering and other controls,it may be possible to consider a refurbishing of treatment materialsemployed in the process chamber. For example, decisions can be madebased upon the contaminant levels (either particles in solution ordissolved chemistries) as to whether it is cost effective to attempt toreclaim the solution in question. For example, it may be observed thatsolvents and rinse solutions contain acceptable levels of chemicalcomponents, but unfortunately carry unacceptably high levels ofcontaminant particles. The solutions in question can be directed throughconventional filtering equipment and retested to certify theiracceptability for re-introduction in subsequent processing stages. Itmay also be possible to perform the same reclamation, by chemicallytreating the solution in question so as to remove or reduce unwanteddissolved chemistries.

Automated instrumentation can also take into account the need formake-up of solutions flowing through tanks 110 or 112, for example.Calculations can be made as to the net effect on ultimate contaminatelevels and it may be possible from time to time to prevent theunnecessary discarding of process solutions by diluting with freshchemistries, thereby providing savings relating not only to the cost ofreplacement solutions but also of waste handling. It will be appreciatedby those skilled in the art that such automated instrumentation can beprovided using conventional techniques, in a space-efficient mannerwhich would not contribute considerably to the space requirements forthe processing equipment.

It will be readily appreciated by those skilled in the art that theoxygen filter (e.g., osmotic membrane degasifier), along with optionalautomated controls, can be used in stand-alone mode to provide a storedquantity of treated aqueous material. Further, the oxygen filter can beincorporated in arrangements other than those shown herein. For example,conventional wafer polishing operations can benefit from theincorporation of the oxygen filter according to principles of thepresent invention, and it will be appreciated in this regard thatsubstantial reduction of wafer handling is thereby made possible. Ifdesired, further advantages may be obtained by combining the oxygenfilter and process chamber of the present invention, incorporating thecombination, for example, in existing wafer processing operations.

If desired, variations in the process chamber are also contemplated bythe present invention. As mentioned above, wafer processing benefitsfrom a light-tight closed environment and a flexibility of operation andreduction in wafer handling has been achieved by incorporating aplurality of different lid arrangements with a common receptacle. It ispossible, however, to adapt the receptacle for continuous, rather thanbatch operations. For example, a conveyor belt can be made to passthrough the process receptacle and can include depressed portions forimmersing articles carried on the conveyor belt beneath fluid levelsmaintained within the receptacle. Such arrangements may be particularlyattractive for photographic operations, for example.

The drawings and the foregoing descriptions are not intended torepresent the only forms of the invention in regard to the details ofits construction and manner of operation. Changes in form and in theproportion of parts, as well as the substitution of equivalents, arecontemplated as circumstances may suggest or render expedient; andalthough specific terms have been employed, they are intended in ageneric and descriptive sense only and not for the purposes oflimitation, the scope of the invention being delineated by the followingclaims.

What is claimed is:
 1. A method for treating opposed major surfaces of asemiconductor device, comprising: providing a treatment chamber defininga cavity for receiving the semiconductor device; providing a carrierfluid; providing an aqueous solution; inserting the semiconductor deviceinto the cavity; passing said aqueous solution and said carrier fluidthrough an osmotic membrane degasifier having a membrane so as to drawoxygen from said aqueous solution through said membrane to said carrierfluid and so as to introduce carrier fluid through said membrane, intosaid aqueous solution so as to control the pH of said aqueous solution;and contacting said semiconductor wafer with aqueous solution from saidosmotic membrane degasifier.
 2. The method of claim 1 further comprisingthe step of drying the said semiconductor device by emptying the cavityof said aqueous fluid and passing heated fluid over the surfaces of saidsemiconductor device.
 3. The method of claim 2 wherein said step ofdrying said semiconductor device further comprises the step of sprayinga rinse chemical on the major surfaces of said semiconductor device. 4.The method according to claim 1 further comprising the steps of:providing a process cover with heater means for heating the processcover; providing a drying cover with means for directing a stream ofdrying gas; providing said treatment chamber with a device openingthrough which said semiconductor device is passed into and out of saidcavity; covering said device opening with said process cover duringtreatment of said semiconductor device; and withdrawing said processcover from said device opening and covering said device opening withsaid drying cover during drying of said semiconductor device.
 5. Themethod according to claim 4 further comprising the steps of monitoringthe oxygen content of said aqueous solution from said osmotic membranedegasifier.
 6. The method according to claim 5 further comprising thestep of controlling the flow of carrier fluid through said osmoticmembrane degasifier in response to measurements of oxygen in saidaqueous solution.
 7. The method according to claim 6 wherein saidcarrier fluid is comprised of a plurality of carrier fluid componentswhich are mixed together to comprise said carrier fluid.
 8. The methodaccording to claim 7 wherein said step of controlling the flow ofcarrier fluid comprises the step of individually controlling the flow ofcarrier fluid components mixed together and inputted into said osmoticmembrane degasifier.
 9. The method according to claim 1 furthercomprising the step of sonically exciting at least one of said treatmentchamber and sid aqueous solution with sonic energy in one of saidultrasonic and said megahertz frequency ranges.
 10. The method accordingto claim 1 further comprising the steps of providing an overflow weirand filling said cavity with aqueous solution so as to immerse saidsemiconductor device with said aqueous solution and so as to overflowaqueous solution through said weir.
 11. The method according to claim 10further comprising the steps of providing a storage tank and couplingthe overflow through said weir to said storage tank.
 12. The method ofclaim 10 further comprising the steps of: providing a plenum defining amixing chamber coupled to said treatment chamber; and the step offilling the cavity with said aqueous solution comprises the step ofpassing aqueous solution through said mixing chamber prior to enteringsaid cavity.
 13. The method of claim 1 further comprising the step ofproviding said carrier fluid with a carbon dioxide component.
 14. Themethod according to claim 12 further comprising the step of withdrawingat least a portion of said aqueous solution from said receptacle inresponse to said counting of particles transferred from saidsemiconductor device to said aqueous solution.
 15. The method accordingto claim 1 further comprising the steps of counting particlestransferred from said semiconductor device to said aqueous solution. 16.The method according to claim 1 further comprising the step of enclosingthe cavity with a cover and introducing a gas blanket in said cavity.17. The method according to claim 16 wherein said gas blanket is atleast partly comprised of carbon dioxide.
 18. The method of claim 1,further comprising the step of introducing acid into said treatmentchamber so as to alter the pH of said aqueous solution.
 19. The methodof claim 18 wherein said step of introducing acid comprises the step ofdripping acid into said treatment chamber.
 20. The method of claim 19further comprising the step of providing a cover connected to saidtreatment chamber and providing acid drip apparatus connected to saidcover for performing the step of dripping acid into said treatmentchamber.